Adenovirus E1A C-terminal CR4 region interacts with the cellular CtBP family proteins, CtBP1 and CtBP2 through a highly conserved sequence motif, PLDLS. CtBP1 and CtBP2 function as transcriptional corepressors and play critical roles during development, oncogenesis and apoptosis regulation in vertebrates. They are functionally redundant for several developmental processes while exerting unique activities with regard to certain other processes. CtBP2 is highly nuclear and CtBP1 is both nuclear and cytosolic. The CtBPs mediate sequence specific transcriptional repression by recruitment of several histone modifying enzymatic constituents such as histone deacetylases, methyl transferases and a histone demethylase. Additionally, the CtBP protein complex also contains E2 and E3 enzymes that mediate SUMO modification of proteins. Adenovirus E1A mutants deficient in interaction with CtBPs exhibit a hyper-transforming phenotype in cooperation with the Ras oncogene. The transformed cells expressing E1A CR4 mutant and the Ras oncogene are highly tumorigenic and metastatic. We hypothesize that interaction of E1A with CtBP might modulate the activities of cellular proteins associated with the N-terminal region of E1A. Additionally, interaction of E1A with CtBP might also cause significant changes in the pattern of cellular CtBP target genes. In Aim 1, we will determine the effects of E1A C-terminal CR4 region and CtBPs on the Ras oncogene cooperating activity of the E1A N-terminal region. Aim 2 will elucidate the unique transcriptional activities of CtBP2 and to determine the effect of E1A on CtBP2- mediated regulation of expression of cellular target genes. Aim 3 will determine the effect of E1A in the cytosolic and nuclear functions of CtBP1. Aim 4 will elucidate the role of CtBP-associated SUMOylation machinery in transcriptional repression. Relevance to Public Health: About one third of all human cancers contain oncogenic mutations in the Ras oncogene. Similarly, the Myc oncogene also plays a dominant role in human malignancies. Certain functions shared by E1A and Myc cooperate with Ras oncogenic transformation while interaction of E1A with CtBP antagonizes such activity. Our proposed studies will harness the knowledge gained from the study of the viral oncoprotein E1A to unravel potential new mechanisms governing oncogenesis and suggest strategies to inhibit the process in humans.